The invention relates to a process for the production of smooth-surfaced parts from a hard gemlike material in accordance with the preamble of claim 1, and a use of this process.
Hard semiprecious-stonelike materials for use as replacements for semiprecious stones and for the production of gemlike products have been disclosed, for example, by Patent Application DE No. 3,445,189. According to this teaching, a binder is mixed with a filler and a base pigment to a pasty consistency. The pasty material is then divided at least once into pieces, coated with an added pigment and subsequently pressed together. This still pasty material is then hardened, either as such or after a further processing step, such as, for example, calendering or other shaping.
In this process, the disadvantage becomes apparent that the surface of the paste material is completely coated by added pigment since the pieces into which the paste material is divided are always recoated with the added pigment. This also applies to the case where the paste material is employed in the form of processable granules. A decorative structure of the finished product can therefore only be seen after removal of the surface. In order to produce such a decorative, for example marble-like, structure on a shaped finished product, for example a watch casing or a knife handle, a further step, for example erosive polishing, is necessary after shaping in order to remove the added pigment coating from the visible surface of the blank and to give this surface the desired character (for example lustre).
However, such erosive polishing is disadvantageous: on the one hand, such a step makes production more expensive, and on the other hand certain shapes, for example those shapes which have recesses and indentations with inside edges, cannot be polished at all or only at very great expense. In addition, polishing accompanied by erosion is particularly disadvantageous in the case of small precision parts such as watch casings: the ideal material density is in the region of the surface of the blanks on the so-called pressing skin, and the deeper the surface layer of a blank is eroded, the more porous the final part appears. In the case of this type of result, it is often necessary to reseal the surface treated by erosive polishing by repeating the pressing.